Search

The complement cascade is a highly sophisticated network of proteins that are well regulated and directed in response to invading pathogens or tissue injury. Complement C3a and C5a are key mediators produced by this cascade, and their dysregulation has been linked to a plethora of inflammatory and autoimmune diseases. Consequently, this has stimulated interest in the development of ligands for the receptors for these complement peptides, C3a receptor, and C5a 1 (C5aR/CD88). In this study we used computational methods to design novel C5a 1 receptor ligands. However, functional screening in human monocyte-derived macrophages using the xCELLigence label-free platform demonstrated altered specificity of our ligands. No agonist/antagonist activity was observed at C5a 1 , but we instead saw that the ligands were able to partially agonize the closely related complement receptor C3a receptor. This was verified in the presence of C3a receptor antagonist SB 290157 and in a stable cell line expressing either C5a 1 or C3a receptor alone. C3a agonism has been suggested to be a potential treatment of acute neutrophil-driven traumatic pathologies, and may have great potential as a therapeutic avenue in this arena. [ABSTRACT FROM AUTHOR]

A peptide contained in the venom of the predatory marine snail Conus tulipa, ρ-TIA, has previously been shown to possess α[sub 1]-adrenoreceptor antagonist activity. Here, we further characterize its pharmacological activity as well as its structure-activity relationships. In the isolated rat vas deferens, ρ-TIA inhibited α[sub 1]-adrenoreceptor-mediated increases in cytosolic Ca[sup 2+] concentration that were triggered by norepinephrine, but did not affect presynaptic α[sub 2]-adrenoreceptor-mediated responses. In radio-ligand binding assays using [[sup 125]I]HEAT, ρ-TIA displayed slightly greater potency at the α[sub 1B] than at the α[sub 1A] or α[sub 1D] subtypes. Moreover, although it did not affect the rate of association for [³H]prazosin binding to the α[sub 1B]adrenoreceptor, the dissociation rate was increased, indicating non-competitive antagonism by ρ-TIA. N-terminally truncated analogs of ρ-TIA were less active than the full-length peptide, with a large decline in activity observed upon removal of the fourth residue of ρ-TIA (Arg[sup 4]). An alanine walk of ρ-TIA confirmed the importance of Arg[sup 4] for activity and revealed a number of other residues clustered around Arg[sup 4] that contribute to the potency of ρ-TIA. The unique allosteric antagonism of ρ-TIA resulting from its interaction with receptor residues that constitute a binding site that is distinct from that of the classical competitive α[sub 1]-adrenoreceptor antagonists may allow the development of inhibitors that are highly subtype selective. [ABSTRACT FROM AUTHOR]